Acoustic positioning with unsynchronized sound sources

The problem In recent years, cellular phones are widely used for GPS-based navigation. There is a growing demand to provide navigation with cellular phones in areas where GPS signals can't be received such as in airports, hospitals, shopping centers and underground parking lots. Furthermore, it is required to provide better than GPS accuracy for locating products in a supermarket, finding rental cars pickup spots or a hotel room door in a corridor.
In this project we created an indoor positioning system for cellular phones, based on unsynchronized acoustic signals. Since all cellular phones can operate at a sampling rate of 44,100 samples per second, we were able to use acoustic signals beyond the human hearing range.